1. Field of the Invention
This invention relates to new and useful improvements in peroxide compositions for use in resin polymerization and to methods of using such compositions.
2. Description of the Prior Art
In the foundry industry, sand is coated with resin binders and formed into molds and cores for the production of precision castings. A wide variety of techniques has been developed for the manufacture of sand cores and molds. These involve the hot box technique for mold and core formation; the shell method; the "No-Bake," and the cold-box technique.
In the hot box and shell methods, sand molds and cores are formed by heating a mixture of sand with a thermosetting resin at a temperature of about 300.degree.-600.degree. F. in contact with patterns which produce the desired shape for the mold or core. The resin is polymerized and a core or mold is formed. Procedures of this type are described in Dunn et al. U.S. Pat. No. 3,059,297 and Brown et al. U.S. Pat. No. 3,020,609.
A particular disadvantage of the hot box and shell methods is the necessity for heating the pattern boxes to 300.degree.-600.degree. F. to polymerize and cure the resin binder. This involves considerable expense and is generally a high cost technique.
The cold box technique for core and mold formation involve the use of sand mixed or coated with resins which may be cured at room temperature by acid or base catalysis. Acid or base catalysts have been used in liquid, solid or gaseous form. Typical cold box processes are shown in Blaies U.S. Pat. No. 3,008,205; Dunn et al. U.S. Pat. No. 3,059,297; Peters et al. U.S. Pat. No. 3,108,340; Kottke et al. U.S. Pat. No. 3,145,438; Brown et al. U.S. Pat. No. 3,184,814; Robins U.S. Pat. No. 3,639,654; Australian Pat. No. 453,160 and British Pat. No. 1,225,984. Many of these processes involve the use of sulfur-containing acid catalyst such as benzene sulfonic acid, toluene sulfonic acid and the like.
A few years ago, a process was developed for room temperature polymerization of condensation resin in which an acid-curing agent is generated in situ in the resin or on a sand-resin mix. It had previously been suggested in U.S. Pat. No. 3,145,438 to inject SO.sub.3 in a form of a gas into a mixture of sand and resin to cure the resin at room temperature. It was found, however, that this process causes an instantaneous curing of the resin in the region subjected to treatment by SO.sub.3 which impedes the diffusion of this gas to other parts of the resin, particularly the central parts of the mixture. Subsequently, a method was developed which avoided this difficulty. In Richard U.S. Pat. No. 3,879,339, it is disclosed that sand may be coated with a suitable oxidizing agent, such as an organic peroxide, and coated with the resin to be used in binding the sand into the form of a core or mold. The sand-resin mixture is then formed into suitable shape and treated with gaseous SO.sub.2. The SO.sub.2 is oxidized, in situ, to SO.sub.3 and converted to sulfur-containing acid by water present in the mixture. The sulfur-containing acid which is generated in situ causes a rapid and uniform polymerization of the resin at room temperature. This process has proved successful commercially and is applicable to phenolic resins, furan resins, and urea-formaldehyde resins, as well as mixtures and copolymers thereof.
In the cold box method of Richard U.S. Pat. No. 3,879,339, there are a large variety of peroxides disclosed which may be added to sand along with resins which are used in forming sand cores or molds. This composition is subsequently formed into shape and treated with gaseous SO.sub.2. The peroxides which are disclosed in the Richard patent are mostly quite expensive and, in many cases, are difficult to handle and to ship or transport. Organic peroxides require special approval for transportation in interstate commerce. Organic peroxides are often highly flammable or present other fire hazards. Organic peroxides also are often shock sensitive and may be explode or detonate under certain conditions. As a result, any and all organic peroxides can not be used in the Richard process because of economic and safety considerations.